This invention relates to a method and apparatus for washing the deck of a press or coater and, more particularly to one having an enclosed doctor blade chamber for metering the solution onto a roll such as a flexographic anilox roll or a gravure roll. For convenience, the ensuing description will be in terms of a flexographic press.
The wash-up of a deck (the fountain and anilox roll) of a flexographic press has been time-consuming and costly. Whenever the ink is changed (for color, consistency, etc.), the old ink must be removed and this is a chore that no one likes. Wash-up has been considered to be the biggest part of a job changeover.
In the past, it has been necessary to circulate up to 20 gallons of solvent to completely clean a deck. The solvent flows through the fountain chamber, being confined by the rotating anilox roll which also requires cleaning. During wash-up, the solids content in the solvent rises to quickly reach an equilibrium so large volumes of solvent have been necessary.
A further complication lies in the fact that to get the job done efficiently, high flow rates are employed, particularly for creating turbulent flow so as to thoroughly cleanse the chamber. However, the end seals normally employed are capable of withstanding only slight pressure, i.e., of the order of 10 to 15" H.sub.2 O. A higher flow rate can cause leakage past the end seals. Therefore, the wash-up job has taken longer than desired.
According to the invention, fresh or once used solvent is drawn into the valve-equipped system while the remaining ink or waste solvent is being pumped into the waste receiver. Once the system has been so charged, valves shift allowing the pump to circulate the solvent through a closed circuit or loop which allows the highly desirable higher flow rates. Also, the pump rotation can be repetitively cycled between forward and reverse directions to enhance the cleaning action of the solvent. The solvent may be any fluid used to dilute the ink components and carry away the ink solids--for example, water for a water-based ink.
The system then may be recharged with fresh solvent where once used solvent has been employed. Thereafter the system is drained of solvent which is replaced by air. In this way nearly all components of the inking system (hoses, pump, anilox roll, doctor blade chamber, valves, fittings, etc.) are automatically cleaned and made ready for the next printing job.
In a preferred embodiment of the invention, it is advantageous to use a solvent saver, i.e., an addition to the system to first circulate once used solvent for a preliminary cleaning of the system. This results in a material reduction of solvent required--from about two gallons per deck to about one gallon.
In this preferred embodiment a fifth valve is employed along with an additional receiver over the basic system. This receiver advantageous has a volume approximately equal to the volume of the system, i.e., volume in the hoses, pump, chamber and valves. Three passages lead from the additional receiver, two return lines and one suction line. The discharge ends of the return lines are positioned above the expected solvent level in the additional receiver whereas the suction line end draws from near the bottom.
In operation, once printing is completed, the system valving is adjusted so as to direct once used solvent from the additional receiver into the system while directing the remaining ink into the waste receiver. Thereafter, the system is closed off to recirculate the once used solvent, thereby scouring the system and converting this heretofore once used solvent to waste solvent. After cycling, the now waste solvent is directed to the waste receiver while fresh solvent is pumped into the system. Prior to introducing ink for a further operation, the new batch of once used solvent is directed into the additional receiver in two stages. A first portion of the system is drained into the additional receiver, the once used solvent being replaced by air from the top of the additional receiver, the second or reverse draining directs the remainder of the once used solvent into the additional receiver while also replacing it with air.
The prior art can be illustrated by U.S. Pat. No. 5,213,044 which has to do with an offset litho press--not a flexographic press. In the lithographic press, there is not a closed ink chamber which precludes washing through repetitive cycles. All that can be done in the litho press is to fill the ink chamber with solvent and drain the same because any attempt to pump solvent through the chamber would result in overflow and loss.
Other objects and advantages of the invention may be seen in the details of the ensuing specification.